1. Field of the Invention
The present invention relates to a control apparatus for an internal combustion engine capable of suppressing an increase in the concentration of NO.sub.x in exhaust gas. Particularly, it relates to such a control apparatus for controlling the concentration of NO.sub.x by controlling a fuel injection quantity, an air-fuel ratio or an ignition timing on the basis of information of a temperature of cylinder.
2. Discussion of Background
FIG. 18 is a diagram showing a conventional air-fuel ratio control apparatus as shown, for instance, in Japanese Unexamined Patent Publication No. 2443/1983. In FIG. 18, a numeral 1 designates an air cleaner, a numeral 2 an air flow meter for measuring an intake air quantity, a numeral 3 a throttle valve, a numeral 4 an intake air manifold, a numeral 5 a cylinder, a numeral 6 a water temperature sensor for detecting a temperature of cooling water, a numeral 8 an exhaust air manifold, a numeral 9 an exhaust gas sensor for detecting the concentration of a component (for instance, oxygen concentration) in exhaust gas, a numeral 10 a fuel injection valve, a numeral 11 an ignition plug, a numeral 15 an air-fuel ratio control apparatus, and a numeral 17 a temperature sensor for exhaust gas.
The operation of the conventional control apparatus will be described. The air-fuel ratio control apparatus 15 receives an intake air quantity signal S1 from the air flow meter 2, a water temperature signal S3 (not shown) from the water temperature sensor 6 and an exhaust gas signal S4 from the exhaust gas sensor 9, when the value of an exhaust gas temperature signal S7 from the exhaust gas temperature sensor 17 is lower than a predetermined value, and outputs a fuel injection signal S5 to the fuel injection valve 10 in order to effect an air-fuel ratio feed-back control.
On the other hand, when an exhaust gas temperature detected by the exhaust gas sensor 17 exceeds a predetermined value in a high temperature zone. The feed-back control is stopped by the air-fuel ratio control apparatus 15 so that an air-fuel ratio is rendered to be smaller (a rich side) than a theoretical air-fuel ratio to thereby avoid an abnormal combustion and thermal deterioration of a catalyst.
In the conventional air-fuel ratio control apparatus having the construction as above-mentioned, accuracy of estimation was poor because a combustion temperature in a cylinder is estimated indirectly from the temperature of exhaust gas. Further, accuracy in an air-fuel control was low because of a low temperature-measuring speed, whereby it was insufficient to prevent generation of NO.sub.x from increasing.
There has been known an apparatus for controlling fuel injection for an internal combustion engine with a fuel injection device as disclosed in, for instance, Japanese Unexamined Patent Publication No. 148636/1981. In such apparatus, however, a fuel injection timing is not always an optimum timing because of the characteristics of an engine to be used when the time of finishing of fuel injection is made in agreement with a predetermined crank angle, with the consequence that the performance of the engine can not sufficiently be obtained with respect to stability of combustion, an engine output and exhaust gas characteristics.